The use of frac balls to control fluid flow in a subterranean well is known, but of emerging importance in well completion operations. The frac balls are generally dropped or injected into a well stimulation fluid stream being pumped into the well. This can be accomplished manually, but the manual process is time consuming and requires that workmen be in close proximity to highly pressurized frac fluid lines, which is a safety hazard. Consequently, frac ball drops and frac ball injectors have been invented to permit faster and safer operation.
Multi-stage well stimulation operations often require that frac balls be sequentially pumped into the well in a predetermined size order that is graduated from a smallest to a largest frac ball. Although there are frac ball injectors that can be used to accomplish this, they operate on a principle of selecting one of several injectors at the proper time to inject the right ball into the well when required. A frac ball can therefore be dropped out of the proper sequence, which has undesired consequences.
As well understood by those skilled in the art, ball drops must also operate reliably in a harsh environment where they are subjected to extreme temperatures, abrasive dust, internal pressure surges, high frequency vibrations, and inclement weather effects including rain, ice and snow.
There therefore exists a need for a controlled aperture ball drop for use during well completion, re-completion or workover operations that substantially eliminates the possibility of dropping a frac ball into a subterranean well out of sequence and that ensures reliable operation in a harsh operating environment.